Rough implementation of the metaballs simulation in MetaballsKit

MetaballsKit/Info.plist

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+<?xml version="1.0" encoding="UTF-8"?>
+<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
+<plist version="1.0">
+<dict>
+	<key>CFBundleDevelopmentRegion</key>
+	<string>en</string>
+	<key>CFBundleExecutable</key>
+	<string>$(EXECUTABLE_NAME)</string>
+	<key>CFBundleIdentifier</key>
+	<string>$(PRODUCT_BUNDLE_IDENTIFIER)</string>
+	<key>CFBundleInfoDictionaryVersion</key>
+	<string>6.0</string>
+	<key>CFBundleName</key>
+	<string>$(PRODUCT_NAME)</string>
+	<key>CFBundlePackageType</key>
+	<string>FMWK</string>
+	<key>CFBundleShortVersionString</key>
+	<string>1.0</string>
+	<key>CFBundleVersion</key>
+	<string>$(CURRENT_PROJECT_VERSION)</string>
+	<key>NSHumanReadableCopyright</key>
+	<string>Copyright © 2017 Eryn Wells. All rights reserved.</string>
+	<key>NSPrincipalClass</key>
+	<string></string>
+</dict>
+</plist>

MetaballsKit/Metaballs.swift

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+//
+//  Metaballs.swift
+//  Metaballs
+//
+//  Created by Eryn Wells on 7/30/17.
+//  Copyright © 2017 Eryn Wells. All rights reserved.
+//
+
+import Foundation
+
+public struct Ball {
+    let radius: CGFloat
+    var position = CGPoint()
+    var velocity = CGVector()
+
+    internal var bounds: CGRect {
+        let diameter = radius * 2
+        return CGRect(x: position.x - radius, y: position.y - radius, width: diameter, height: diameter)
+    }
+
+    init(radius r: CGFloat) {
+        radius = r
+    }
+
+    internal mutating func update() {
+        position.x += velocity.dx
+        position.y += velocity.dy
+    }
+}
+
+public struct Field {
+    var size: CGSize
+    private(set) var balls = [Ball]()
+
+    internal var bounds: CGRect {
+        return CGRect(origin: CGPoint(), size: size)
+    }
+
+    init(size s: CGSize) {
+        size = s
+    }
+
+    public func update() {
+        let selfBounds = bounds
+        for var ball in balls {
+            // Update position of ball.
+            ball.update()
+
+            if !selfBounds.contains(ball.position) {
+                // Degenerate case. If the ball finds itself outside the bounds of the field, plop it back in the center.
+                ball.position = CGPoint(x: selfBounds.midX, y: selfBounds.midY)
+            } else {
+                // Do collision detection with walls.
+                let ballBounds = ball.bounds
+                if !selfBounds.contains(ballBounds) {
+                    if ballBounds.minX < selfBounds.minX || ballBounds.maxX > selfBounds.maxX {
+                        ball.velocity.dx *= -1
+                    }
+                    if ballBounds.minY < selfBounds.minY || ballBounds.maxY > selfBounds.maxY {
+                        ball.velocity.dy *= -1
+                    }
+                }
+            }
+        }
+    }
+
+    public func sample(at point: CGPoint) throws -> CGFloat {
+        return 0.0
+    }
+
+    public mutating func add(ball: Ball) throws {
+        guard bounds.contains(ball.bounds) else {
+            /// TODO: Throw an error.
+            return
+        }
+        balls.append(ball)
+    }
+}

MetaballsKit/MetaballsKit.h

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+//
+//  MetaballsKit.h
+//  MetaballsKit
+//
+//  Created by Eryn Wells on 7/30/17.
+//  Copyright © 2017 Eryn Wells. All rights reserved.
+//
+
+#import <Cocoa/Cocoa.h>
+
+//! Project version number for MetaballsKit.
+FOUNDATION_EXPORT double MetaballsKitVersionNumber;
+
+//! Project version string for MetaballsKit.
+FOUNDATION_EXPORT const unsigned char MetaballsKitVersionString[];
+
+// In this header, you should import all the public headers of your framework using statements like #import <MetaballsKit/PublicHeader.h>
+
+